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Forces: Why Things Move

Intermediate · 11 lessons · Free, no account needed

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Lessons

1. Forces Are Pushes and Pulls (5 min): A force is a push or a pull, measured in newtons (N). It always has a direction.
2. Things Keep Going: Inertia (7 min): A moving thing keeps moving at the same speed in a straight line unless a force changes that. This is Newton's first law.
3. F = ma (7 min): Newton's second law: net force = mass × acceleration, F = ma.
4. Mass vs Weight (7 min): Mass (kg) is how much stuff, and how hard it is to speed up. It is the same on every world.
5. Friction (7 min): Friction is the force between surfaces that resists sliding. It points against the motion, or against the pull.
6. Free-Body Diagrams (7 min): A free-body diagram shows one object alone, with an arrow for every force on it and nothing else.
7. Every Push Has a Partner (7 min): Newton's third law: when A pushes or pulls B, B pushes or pulls A just as hard, in the opposite direction.
8. Air Resistance and Terminal Velocity (7 min): Air resistance (drag) pushes against motion through air, and it grows with speed.
9. Turning Needs a Force (7 min): To move in a circle, something must keep pulling or pushing the object toward the centre: the centripetal force.
10. Apparent Weight: Elevators and Rides (7 min): A scale measures the support force that pushes you up, not your mass. In a lift it reads N = m (g + a).
11. Project: Lunar Lander (8 min): A lander hovers when thrust equals weight: T = m g, 3240 N for 2000 kg on the Moon.

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